Variable area nozzle assisted gas turbine engine restarting

ABSTRACT

An example turbofan engine restarting system includes a core nacelle housing, a compressor, and a turbine. The core nacelle is disposed within a fan nacelle. A bypass flowpath downstream from the turbofan is arranged between the two nacelles. A controller is programmed to manipulate the nozzle exit area of the bypass flowpath to facilitate startup of the engine. In one example, the controller manipulates the nozzle exit area using hinged flaps in response to an engine shutdown condition. The flaps open and close to adjust the nozzle exit area and the associated bypass flow rate, the mass flow rate of the air through the core nacelle and the rotational speed of the compressor rotor.

BACKGROUND OF THE INVENTION

This invention relates to starting gas turbine engines, and, moreparticularly, to facilitating gas turbofan engine restarts byeffectively altering the nozzle exit area.

Gas turbine engines are widely known and used for power generation andvehicle (e.g., aircraft) propulsion. During in-flight propulsion of amulti-engine aircraft, certain problems may occur with one enginecausing the engine to shut down. For example, inclement weather,non-optimum trimming of engine idle, fuel nozzle coking, fuelcontamination, loss of electric power, fuel mismanagement, pilot error,or the like may, under certain conditions, warrant voluntary orautomatic shut down of an engine. Although the remaining engines cantypically fly the aircraft, it is ordinarily desired to restart the shutdown engine while the aircraft is still in-flight.

An engine restart envelope includes combinations of aircraft altitudeand airspeed that provide a suitable air supply to the engine sufficientfor restarting. When traveling outside of the engine restart envelope,the air supply to the engine may not contain enough oxygen to supportcombustion during ignition. In some instances, starter-assistance may beused to increase the rotational speed of a fan section of the engine,which increases altitude and airspeed combinations suitable forrestarting the engine. Increasing the rotational speed of the fansection draws additional airflow into the engine and, in so doing,augments the supply of oxygenated air supporting combustion.

Disadvantageously, at certain combinations of altitude and airspeed,increasing the rotational speed of the fan section is not alonesufficient to generate adequate airflow to support combustion. As aresult, aircraft experiencing in-flight shutdown may have to rapidlyadjust altitude and/or airspeed to move within the engine restartenvelope or starter-assisted engine restart envelope. As an example, ifan engine requires restart in aircraft traveling at an altitudeunsuitable for engine restarts, the aircraft may rapidly decreaseelevation to move to an altitude suitable for restarting the turbofanengine. Alternatively, the aircraft may be forced to continue flying,without propulsion from the shutdown engine.

What is needed is a method capable of restarting the turbofan enginethrough an increased number of altitudes and airspeeds.

SUMMARY OF THE INVENTION

An example turbofan engine starting system includes a core nacellehousing a compressor and a turbine. The core nacelle is disposed withina fan nacelle. The fan nacelle includes a turbofan. A bypass flow pathdownstream from the turbofan is arranged between the two nacelles. Acontroller is programmed to manipulate the nozzle exit area tofacilitate startup of the engine. In one example, the controllermanipulates the nozzle exit area using hinged flaps in response to anengine shutdown condition. The hinged flaps open and close to adjust thenozzle exit area and the associated bypass flow rate.

An example method for starting the engine includes detecting an engineshutdown and changing the effective nozzle exit area during a restartprocedure to facilitate restarting the engine. In one example, themethod includes adjusting the nozzle exit area to increase thewindmilling speed of a fan section of the turbofan engine and decreasingthe nozzle exit area to increase the mass flow rate of air through thecore nacelle.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows.

FIG. 1 illustrates selected portions of an example gas turbine enginesystem.

FIG. 2 illustrates a variable air nozzle and coolant passage within thegas turbine engine system shown in FIG. 1.

FIG. 3 illustrates an example turbofan engine restart envelope withoutassistance from a variable area nozzle.

FIG. 4 illustrates an example turbofan engine restart envelope withassistance from a variable area nozzle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A geared turbofan engine 10 is shown in FIG. 1. The engine 10 includes acore nacelle 12 that houses a low rotor 14 and high rotor 24. The lowrotor 14 supports a low pressure compressor 16 and low pressure turbine18. In this example, the low rotor 14 drives a fan section 20 through agear train 22. The high rotor 24 rotationally supports a high pressurecompressor 26 and high pressure turbine 28. A combustor 30 is arrangedbetween the high pressure compressor 26 and high pressure turbine 28.The low and high rotors 14, 24 rotate about an axis X. At least aportion of the core nacelle 12 is disposed within a fan nacelle 34.

In the examples shown, the engine 10 is a high bypass turbofanarrangement. In one example, the bypass ratio is greater than 10, andthe turbofan diameter is substantially larger than the diameter of thelow pressure compressor 16. The low pressure turbine 18 has a pressureratio that is greater than 5, in one example. The gear train 22 can beany known suitable gear system, such as a planetary gear system withorbiting planet gears, planetary system with non-orbiting planet gears,or other type of gear system. It should be understood, however, that theabove parameters are only exemplary of a contemplated geared turbofanengine. That is, the invention is applicable to other types of engines.

For the engine 10 shown FIG. 1, a significant amount of thrust may beprovided by the bypass flow B due to the high bypass ratio. Thrust is afunction of density, velocity, and area. One or more of these parameterscan be manipulated to vary the amount and direction of thrust providedby the bypass flow B. In one example, the engine 10 includes a nozzlestructure 38 associated with the nozzle exit area A to change thephysical area and geometry to manipulate the thrust provided by thebypass flow B. However, it should be understood that the nozzle exitarea A may be effectively altered by other than structural changes, forexample, by altering a boundary layer of the bypass flow B. Furthermore,it should be understood that effectively altering the nozzle exit area Ais not limited to physical locations approximate to the exit of the fannacelle 34, but rather, includes altering the bypass flow B by anysuitable means at any suitable location of the fan section 20.

In the example shown in FIG. 2, an engine restart system 54 includesmultiple hinged flaps 42 arranged circumferentially about the rear ofthe fan nacelle 34. The hinged flaps 42 form a portion of a controldevice 41, which further includes a controller 50 in communication withactuators 46 used to manipulate the hinged flaps 42. A detector 52communicates information about the engine 10 to the controller 50, forexample, information that the engine 10 has shut down or relating to thestartup state of the engine 10. In one example, the detector 52 monitorsthe rotational speed of the low rotor 14, which is indicative of thestate of the engine 10. The controller 50 interprets rotational speedsof the low rotor 14 below a certain level as a condition of the engine10 indicting the engine 10 has shut down. In another example, thedetector 52 monitors fuel consumption of the engine 10. If the engine 10experiences a drop in fuel consumption, the detector 52 communicatesthis information to the controller 50, which interprets the informationas a shutdown of the engine 10. The detector 52 may be located proximateor apart from the engine 10. The controller 50 also communicates with adriver 56, which may be controlled by an aircraft operator. Thus, thecontroller 50 may operate automatically using information from thedetector 52, or may operate manually based on signals from the driver56. A starter 58, such as a hydraulic starter, may be used to boost therotational speed of the fan section 20.

The hinged flaps 42 can be actuated independently and/or in groups usingsegments 44. The segments 44 and individual hinged flaps 42 can be movedangularly using actuators 46. The control device 41 thereby varies thenozzle exit area A (FIG. 1) between the hinged flaps 42 and the engine10 by altering positions of the hinged flaps 42. In a closed position,the hinged flap 42 is closer to the core nacelle 12 for a relativelysmaller nozzle exit area A. In an open position, the hinged flap 42 isfarther away from the core nacelle 12 for a relatively larger nozzleexit area A.

When the engine 10 shuts down during flight, the fan section 20 willcontinue to rotate, or windmill, as the engine 10 moves, either bygliding or powered by additional engines. Restarting the engine 10requires adequate compressed air to support combustion. Changing thenozzle exit area A influences the mass flow rate of airflow over the fansection 20 as a function of radial distance from the axis X. Forexample, increasing the size of the nozzle exit area A increases thebypass flow B. This decreases the mass flow rate of the airflow over thefan section 20 at radial distances near to the axis X and increases themass flow rate of the airflow over the fan section 20 at radialdistances away from the axis X. The increased mass flow rate exerts moreforce on radially outward portions of the fan section 20 to acceleraterotation of the fan section 20. Thus, by controlling bypass flow B therotational speed of the fan section 20 is controlled.

As an example, it is estimated that moving the hinged flaps 42 from alocation suitable for aircraft cruising operations to an open positionincreases the windmilling speed of the fan section 20 about 10-20%.Increasing the windmilling speed of the fan section 20 also increasesthe rotational speed of the low rotor 14, the low speed compressor 16,and the low pressure turbine 18.

Inversely, decreasing the size of the nozzle exit area A increases themass flow rate of the air through the core nacelle 12. As a result,after increasing the fan section 20 windmilling speed, the hinged flaps42 move to a closed position to decrease the nozzle exit area A andthereby increase airflow through the core nacelle 12. Rotational inertiaof the fan section 20 forces airflow into the core nacelle 12. Therotational inertia also contributes to rotating the low pressurecompressor 16, which compresses air in preparation for ignition. In thisexample, the controller 50 monitors the rotational speed of the lowrotor 14 to determine an appropriate time to decrease the size of thenozzle exit area A.

In an example method of restarting the engine 10, communications fromthe controller 50 open the hinged flaps 42 to maximize the windmillingspeed of the rotating fan section 20, which also increases therotational speed of the low rotor 14. Next, communications from thecontroller 50 direct the hinged flaps 42 to close, which increases themass flow rate of airflow through the core nacelle 12. Rotationalinertia remaining in the windmilling fan section 20 helps to compressthe increased airflow through the core nacelle 12. If not for therotational inertia in the windmilling turbofan, airflow would only movethrough the engine 10 at a rate corresponding to the closed position ofthe hinged flaps 42. The rotational inertia in the windmilling fansection 20 increases airflow above this rate increasing the supply ofoxygenated air available for combustion. Actuating the hinged flaps 42in this way during the engine 10 restart increases the combinations ofaltitudes and airspeeds suitable for restarting the engine 10. Afterreaching a sufficient level of compressed air, fuel flow is introducedto the compressed air, and the mixture is ignited, thereby restartingthe engine 10.

Referring now to FIG. 3 with continued reference to FIG. 1, illustratedis a typical flight envelope 60 for the engine 10, that is, thosecombinations of altitude and airspeed suitable for operating the engine10. Within the flight envelope 60, an area 64 represents combinations ofaltitude and speed suitable for restarting the engine withouteffectively altering the nozzle exit area A. FIG. 4 represents anincreased area 68 illustrating the combinations of altitude and speedsuitable for restarting the typical engine when altering the nozzle exitarea A. Formerly, the engine 10 may have needed starter assistance torestart at some of the altitudes and speeds included in area 68. Ofcourse, starter assistance may increase the likelihood of restarting theengine 10 at altitudes and airspeeds beyond those included in area 68.

In the disclosed examples, the ability to control the amount of airflowthrough the nozzle exit area A provides the benefit of restarting theengine 10 while in flight at increased combinations of altitudes andairspeeds. Restarts in prior designs may have required starterassistance for similar restarts. Further, although described in terms ofrestarts while in the air, adjusting nozzle exit area A (FIG. 1) mayalso be used to facilitate starting the engine 10 while on the ground.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art may recognize certain modificationsfalling within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope ofcoverage for this invention.

What is claimed is:
 1. A turbofan engine restarting system, comprising:a core nacelle housing a compressor and a turbine; a fan nacelle housinga fan section that is arranged upstream from said core nacelle; and abypass flow path downstream from said fan section and arranged betweensaid core and fan nacelles, said bypass flow path including an effectivenozzle exit area that defines an axis; a controller programmed toselectively increase and decrease said effective nozzle exit area tofacilitate restart of said engine during flight in air; and a starterfor increasing a rotational speed of said fan section.
 2. A method ofrestarting a turbofan engine comprising the steps of: a) detecting ashutdown of a turbofan engine during flight in air; b) selectivelyincreasing and decreasing an effective nozzle exit area from a bypassflow path within the engine in response to the shutdown during a flightin air to establish a desired condition for a startup of the engineduring the flight in air; and c) increasing the rotational speed of afan section of the engine using a starter.
 3. A turbofan enginerestarting system, comprising: a core nacelle housing a compressor and aturbine; a fan nacelle housing a fan section that is arranged upstreamfrom said core nacelle; and a bypass flow path downstream from said fansection and arranged between said core and fan nacelles, said bypassflow path including an effective nozzle exit area that defines an axis;at least one nozzle flap disposed on said fan nacelle operative tocontrol said effective nozzle exit area; and a controller programmed toselectively increase and decrease said effective nozzle exit area tofacilitate restart of said engine during flight in air, wherein saideffective nozzle exit area is increased when said effective nozzle exitarea is not a maximum effective nozzle exit area.
 4. A method ofrestarting a turbofan engine comprising the steps of: a) detecting ashutdown of a turbofan engine during flight in air; b) selectivelyincreasing and decreasing effective nozzle exit area from a bypass flowpath within the engine in response to the shutdown during a flight inair to establish a desired condition for a startup of the engine duringthe flight in air; c) actuating a plurality of individual flaps radiallyaway from an axis of the turbofan engine to increase said effectivenozzle exit area, and actuating the plurality of individual flapsradially toward the axis to decrease said effective nozzle exit area,wherein the increasing occurs when the effective nozzle exit area of thebypass flow path is not a maximum effective nozzle exit area of thebypass flowpath.